This invention relates generally to implantable infusion ports of type utilized for frequent administration of medication to a patient. More particularly, this invention relates to an improved infusion port designed with a reduced or minimal internal volume to provide substantially maximum delivery of medication to the patient, with minimal residual medication remaining within the infusion port.
Implantable infusion ports are generally known in the art to include a relatively compact and generally cup-shaped housing having a resilient self-sealing septum mounted over the open end thereof to define a medication receiving chamber. The housing and septurn are surgically implanted into the body of a patient at a position closely underlying the skin and subcutaneous tissue, and with the septum presented toward the patient's skin. The infusion port is adapted for palpable identification through the skin to receive medication in liquid form injected via a hypodermic needle or cannula through the skin and septum into the medication chamber. A catheter mounted on the housing communicates with the medication chamber to deliver the medication to a selected site within the patient. In this regard, the catheter is often placed for delivering the medication to the patient's vascular system, whereby such implantable infusion ports are sometimes referred to as vascular access devices.
Implantable infusion ports of this general type are typically used to facilitate injection or infusion of medication in liquid form on a frequent basis. More specifically, the implanted port can be accessed transcutaneously with a hypodermic needle or the like on a frequent and repeated basis, and over an extended period of time, with minimal patient discomfort. The infusion port provides accurate delivery of medication to a specific delivery site within the patient, without complications associated with repeated intravenous puncture or the infection risk associated with a transcutaneous catheter. One common application for an implantable infusion port is the administration of chemotherapy agents. Delivery of other medications such as insulin, pain medication, etc., on a frequent basis has also been proposed.
To insure accurate delivery of the selected medication to the internal chamber of an implanted infusion port, the self-sealing septum has been designed with a substantial surface area for accurate palpable identification through the skin of the patient. In addition, to ensure fully seated reception of the typically chisel-tipped injection needle, the medication chamber has been designed with a substantial depth dimension. Unfortunately, these design factors inherently require the medication chamber of the infusion port to have a substantial internal volume, especially in comparison with relatively small volume doses of medication to be administered to the patient. As a result, when medication is injected into the chamber, a potentially significant quantity of the medication is required to fill the volume of the chamber before any medication is in fact delivered to the patient. Moreover, at the conclusion of an injection step, a significant quantity of the medication will remain as a residue within the internal chamber of the infusion port. Although such residue medication may be dislodged and delivered to the patient at a later time in the course of a sub sequent injection step, degradation can occur quickly with some medicaments such that the effectiveness is reduced or lost. While it is often possible to compensate for the degraded and ineffective medication residue by simply increasing the dose injected into the infusion port chamber, the relatively high cost of many medications makes increased dosages undesirable.
There exists, therefore, a significant need for improvements in implantable infusion ports, particularly with respect to maximizing the quantity of injected medication which is actually and immediately administered to the patient, while concurrently minimizing the presence of residual medication in the infusion port. The present invention fulfills these needs and provides further related advantages.